Move config binary and GHC intermediate outputs to cacheDir

That's where they belong. As XDG was more or less broken in previous
xmonad releases, we can assume few people use it so now's the best time
to move files around.

For users of `~/.xmonad`, this only causes intermediate outputs (.o,
.hi) to go elsewhere.

Fixes: https://github.com/xmonad/xmonad/issues/178

CHANGES.md

@@ -29,6 +29,10 @@
     In the cases of 1. and 3., the build script or executable is
     expected to be in the config dir.
 
+    Additionally, the xmonad config binary and intermediate object files were
+    moved to the cache directory (only relevant if using XDG or
+    `XMONAD_CACHE_DIR`).
+
   * Change `ScreenDetail` to a newtype and make `RationalRect` strict in
     its contents.
 

INSTALL.md

@@ -356,13 +356,13 @@ exec xmonad
 in your `~/.xinitrc`, you would write
 
 ``` shell
-exec $HOME/.local/share/xmonad/xmonad-x86_64-linux
+exec $HOME/.cache/xmonad/xmonad-x86_64-linux
 ```
 
-The `~/.local/share` prefix is the `$XDG_DATA_DIR` directory.  Note that
+The `~/.cache` prefix is the `$XDG_CACHE_HOME` directory.  Note that
 if your xmonad configuration resides within `~/.xmonad`, then the
 executable will also be within that directory and not in
-`$XDG_DATA_DIR`.
+`$XDG_CACHE_HOME`.
 
 [XDG]: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
 [git]: https://git-scm.com/

src/XMonad/Core.hs

@@ -480,8 +480,7 @@ runOnWorkspaces job = do
 -- the following purposes:
 --
 -- * @dataDir@: This directory is used by XMonad to store data files
--- such as the run-time state file and the configuration binary
--- generated by GHC.
+-- such as the run-time state file.
 --
 -- * @cfgDir@: This directory is where user configuration files are
 -- stored (e.g, the xmonad.hs file).  You may also create a @lib@
@@ -489,7 +488,9 @@ runOnWorkspaces job = do
 -- command will add it to the GHC include path.
 --
 -- * @cacheDir@: This directory is used to store temporary files that
--- can easily be recreated.  For example, the XPrompt history file.
+-- can easily be recreated such as the configuration binary and any
+-- intermediate object files generated by GHC.
+-- Also, the XPrompt history file goes here.
 --
 -- For how these directories are chosen, see 'getDirectories'.
 --
@@ -565,12 +566,17 @@ getXMonadDataDir :: X String
 getXMonadDataDir = asks (dataDir . directories)
 {-# DEPRECATED getXMonadDataDir "Use `asks (dataDir . directories)' instead." #-}
 
-binFileName, errFileName, stateFileName, srcFileName, libFileName :: Directories -> FilePath
-binFileName   Directories{ dataDir } = dataDir </> "xmonad-" <> arch <> "-" <> os
+binFileName, buildDirName :: Directories -> FilePath
+binFileName  Directories{ cacheDir } = cacheDir </> "xmonad-" <> arch <> "-" <> os
+buildDirName Directories{ cacheDir } = cacheDir </> "build-" <> arch <> "-" <> os
+
+errFileName, stateFileName :: Directories -> FilePath
 errFileName   Directories{ dataDir } = dataDir </> "xmonad.errors"
 stateFileName Directories{ dataDir } = dataDir </> "xmonad.state"
-srcFileName   Directories{  cfgDir } =  cfgDir </> "xmonad.hs"
-libFileName   Directories{  cfgDir } =  cfgDir </> "lib"
+
+srcFileName, libFileName :: Directories -> FilePath
+srcFileName Directories{ cfgDir } = cfgDir </> "xmonad.hs"
+libFileName Directories{ cfgDir } = cfgDir </> "lib"
 
 buildScriptFileName, stackYamlFileName :: Directories -> FilePath
 buildScriptFileName Directories{ cfgDir } = cfgDir </> "build"
@@ -664,6 +670,7 @@ compile dirs method =
               , "-fforce-recomp"
               , "-main-is", "main"
               , "-v0"
+              , "-outputdir", buildDirName dirs
               , "-o", binFileName dirs
               ]